Dud panel, or what

[la7qz]

Good afternoon folks (It's always afternoon somewhere...

I've come across a weird problem on a catamaran out here in the sun.

The boat has two KC-120 1 panels mounted horizontally side by side. One panel is putting out around 4 amps with relatively low sun, the other is putting out between 0.8 and 1.5A.

Testing shows open circuit voltage from each panels independently around 19V and short circuit current for each panels is around 5A at the time of testing. There is some shading from the rigging, but this is the same for both panels. The owner says he rarely sees more than 5A out of the pair even in the middle of the day with the sun overhead.

My initial reaction is that the low output panel is a dud, but why do we still see good short circuit current on both panels.

Oh, incedentally, there is an identical pair of panels the other side of the boat with the exact same problem. One panel producing what I would expect, the other with much lower output, but I haven't started testing on that side yet, so no numbers available.

Any ideas would be very welcome.

Regards,

Owen, the Magic Sailor

Yacht Magic

St Maarten

[electronbaby]

depends on how the strings are wired and oriented.

There are known problems with KC120's. They had a large batch of failures due to the internal solder tabs opening up. This is visible from the front of the module. Look for any browning around the top and bottom of the module. It might show correct ISC initially until heat starts to be dissipated in the circuit, and then it will open on you, and you will lose one of the series strings in each module that has the failure, effectively cutting your current substantially (there are two series strings of cells in each module with a bypass diode on each).

If your mods are good, then check the shading characteristics of your mounting technique.

If you find a bad module, contact Kyocera, and they will issue you remanufactured units from their Mexico plant. They used to replace them with brand new KC130's, but those days are gone unfortunately.

Ive seen many types of modules fail. Ive seen this happen to BP and most often in Kyocera. Kyocera's new modules are drastically improved however.

Just some thoughts...

[richhagen]

It would seem to make sense if one of the two strings of cells had an open circuit as Roy has pointed out.  I have seen a similar effect on a single string panel where one of the cells developed a crack in the solar cell, apparently reducing its ability to conduct current, but not effecting the open circuit voltage of the panel.  Good luck, Rich Hagen

[Ungrounded Lightning Rod]

I'd suspect the shadow.

The current is proportional to the amount of light.  The cell (or parallel group of cells) with the least current output controls the current output of the panel.  So a shadow over part of one cell can cause a drastic drop in the panel's current output.

It's doubly suspicious since you have similar symptoms for the other side.

Take a close look at the shadow and see if it is covering most of one cell on the lower panel and only part of any given cell on the upper one.

If this is the problem the fix is obviously to rearrange the panel mounting to eliminate any wide shadows.  (Shadows of the lines should be OK.  Blocks, spreaders, and other wide stuff not.)

[la7qz]

Hi again

After writing, I tested the panels on the port side of the catamaran and found the same issue. Good short circuit amps on both panels, but very low output on one of them. We rearranged the panels so that the two good ones are on the starboard side and the two bad ones are on the port side. We now have normal output on the starboard side and next to nothing on port. I believe this proves that we have two dud panels. We did find browning around one of the solder joints at one end of one of the panels as described by Electronbaby and the same joint on the other panel looked suspect, but with no browning.

I am aware of the shading issues which are always a problem on a sailboat. I live off 99% RE on a sailboat myself (still burning hydrocarbons to cook and heat shower water), but on a moving boat (and with a moving sun) there should be some time where at least one pair of panels have full sun and give full output. In this case, the owner never saw more than 5A from one pair of KC 120 panels even with the sun directly overhead and no shading on the panels. After rearranging the panels yesterday, we were seeing 7A late in the afternoon from the starboard side. It will be interesting to see what happens today if it is sunny around midday.

Thanks guys. The owner will be contacting Kyocera.

Regards,

Owen Morgan

Yacht Magic

St Maarten

[Opera House]

Panels that have two strings of cells in parallel can exhibit this problem.  One of the strings can have shorted cells. Example: one string produces 17 volts and the other produces 13 volts.  The open circuit voltage reads the highest string.  In short circuit it produces normal amps since the cells are basically a current source.  As the voltage the cells source to, the current then drops.  Exactly what you are seeing.

[ghurd]

Not a great solution, but it may get him some power from the faulty bank while sorting out the details with Kyocera.

Connect the panels in series, for 24V use.

Feed the output directly to the battery bank.  Do Not use a controller.  40Voc will smoke the controller.

With luck, each PV only has one fault.  The bypass diodes bypass the bad sections in each PV, leaving something about like one good 12V PV.

Might get him 5A.  Worth a try.

G-

[Ungrounded Lightning Rod]

We rearranged the panels so that the two good ones are on the starboard side and the two bad ones are on the port side. We now have normal output on the starboard side and next to nothing on port. I believe this proves that we have two dud panels.

Yep!  That's definitive, all right.